Method for operating an internal combustion engine

ABSTRACT

A method for operating an internal combustion engine having at least one triggerable intake valve and at least one triggerable discharge valve, in which the internal combustion engine is directly started in a start-up operating mode and, following the start, is operated in at least one other operating mode. A starting discharge instant of a discharge valve of the internal combustion engine that is used during the start-up operating mode is retarded in time with respect to a standard discharge instant so as to improve the direct start-up characteristics of the internal combustion engine. In addition, to further improve the direct start-up characteristics, it is possible to retard a closing instant of an intake valve that is used during the start-up operating mode with respect to a standard closing instant.

FIELD OF THE INVENTION

The present invention relates to a method for operating an internalcombustion engine having at least one triggerable intake valve and atleast one triggerable discharge valve, in which the internal combustionengine is directly started in a start-up operating mode and, after thestart, is operated in at least one other operating mode. Furthermore,the present invention relates to an internal combustion engine having atleast one triggerable intake valve and at least one triggerabledischarge valve, which is started directly in a start-up operating modeand is operated in at least one other operating mode after the start.

Furthermore, the present invention relates to a control device for ageneric internal combustion engine as well as a computer program for thecontrol device.

BACKGROUND INFORMATION

The principle of a direct start of internal combustion engines, i.e.,the starting of the internal combustion engine without electricalstarter or similar device, is known.

To allow a reliable direct start-up of an internal combustion enginefrom standstill, fuel must be injected into the particular combustionchamber of a cylinder of the internal combustion engine that happens tobe in a power stroke at that time. In the subsequent ignition of theinjected fuel, the pressure in the cylinder rises and drives a piston ofthe cylinder, which outputs action via a crankshaft.

SUMMARY OF THE INVENTION

It is an objective of the present invention to further develop a genericoperating method as well as an internal combustion engine and a controldevice for it, in such a way that a simple and reliable direct start-upof the internal combustion engine is ensured.

According to the present invention, this objective is achieved in anoperating method of the type mentioned at the outset in that a startingdischarge instant of the discharge valve, which is used during thestart-up operating mode for the discharge of waste gases of the internalcombustion engine, is time-retarded relative to a standard dischargeinstant used during the additional operating mode(s), and/or in that aclosing instant of the intake valve for the aspiration of fresh gas usedduring the start-up-operating mode is time-retarded with respect to astandard closing instant used during the additional operating mode(s).

Retarding the starting discharge instant according to the presentinvention relative to the standard discharge instant has the result thatthe combustion energy released during the first combustion in the directstart-up of the internal combustion engine is able to be converted intomechanical action in a more optimal manner, the mechanical action beingable to be utilized to start the internal combustion engine. This willensure that the largest possible portion of the combustion energy isused to start the internal combustion engine.

Another positive effect resulting in the operating method according tothe present invention is the lowering of a compression pressure in acombustion chamber of the individual cylinder of the internal combustionengine. This lowering results from the reduced air requirement caused bythe retarding of the closing instant of the intake valve in the start-upoperating mode.

The retardation of the starting discharge instant according to thepresent invention, together with the retardation of the closing instant,is able to be utilized in the start-up operating mode. It is alsopossible to utilize either only the retardation of the startingdischarge instant or the retardation of the closing instant in thestart-up operating mode.

In the case of valve-gear systems having camshaft(s), the presentinvention proposes that the retardation be implemented by adjusting adischarge-camshaft that triggers the discharge valve and/or anintake-camshaft that triggers the intake valve. According to anadditional specific embodiment of the operating method of the presentinvention, phase actuators, in particular, are used to adjust thecamshaft(s). In this context, it is also conceivable to simultaneouslytrigger an intake camshaft and a discharge camshaft using one phaseactuator.

Another specific embodiment of the present invention provides that, asan alternative to the phase actuator or in parallel thereto, avalve-gear system that influences the opening time of the intakevalve/discharge valve be used to adjust the intake camshaft and/or thedischarge camshaft.

Another, very advantageous specific embodiment of the present inventionprovides that the intake camshaft and/or the discharge camshaft bealready adjusted for a subsequent start in the start-up operating modeupon deactivation of the internal combustion engine. This dispenses withthe requirement of adjusting the camshaft(s) immediately prior to thenext start.

According to another specific embodiment of the method according to thepresent invention, the intake valve and/or the discharge valve are/istriggered by a camshaft-free valve-gear system, i.e., in anelectromagnetic or hydraulic manner, for example. The retardation of thestarting discharge instant and the closing instant according to thepresent invention is also possible thereby and may generally even berealized at a lower mechanical effort.

Another, very advantageous specific embodiment of the method accordingto the present invention provides for a valve lift of the intake valveor the discharge valve to be varied, which makes it possible to furtherimprove the direct-start characteristics of the internal combustionengine.

Another specific embodiment of the present invention in which theretardation is reduced in a stepwise manner with increasing rotationalspeed of the internal combustion engine, is very advantageous as well.It is also possible to deactivate the retardation once a predefinableminimum speed of the internal combustion engine has been exceeded, thatis to say, without a stepwise reduction.

As a further achievement of the objective of the present invention, itis proposed for a generic internal combustion engine and for a genericcontrol device that a starting discharge instant of the discharge valve,which is used during the start-up operating mode for the discharge ofwaste gases of the internal combustion engine, be time-retarded relativeto a standard discharge instant that is used during the additionaloperating mode(s), and/or that a closing instant of the intake valve,which is used during the start-up operating mode for the aspiration offresh gas, be time-retarded relative to a standard closing instant thatis used during the additional operating mode(s).

As an additional further achievement of the object of the presentinvention, a computer program for a generic control device is providedas well.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 through 8 in each case a valve-trigger diagram according to aspecific embodiment of the present invention.

FIG. 9 a state diagram of a specific embodiment of the method accordingto the present invention.

FIG. 10 a schematic illustration of an internal combustion engineaccording to the present invention.

DETAILED DESCRIPTION

FIG. 10 shows an internal combustion engine 1 of a motor vehicle inwhich a piston 2 is able to be moved back and forth in a cylinder 3.Cylinder 3 is provided with a combustion chamber 4, which is delimited,among others, by piston 2, a triggerable intake valve 5 and atriggerable discharge valve 6. The triggering of intake valve 5 anddischarge valve 6 is implemented via electromagnetic actuators, whichare not shown in FIG. 10, thereby allowing a flexible adjustment of theintake and discharge instants. Coupled to intake valve 5 is an intakemanifold 7, and coupled to discharge valve 6 is a discharge pipe 8.

In the region of intake valve 5 and of discharge valve 6, a fuelinjector 9 and a spark plug 10 project into combustion chamber 4. Fuelis able to be injected into combustion chamber 4 via injector 9. Thefuel in combustion chamber 4 may be ignited by spark plug 10.

A rotatable throttle valve 11 through which air may be supplied tointake manifold 7 is disposed in intake manifold 7. The supplied airquantity is a function of the angle setting of throttle valve 11. Acatalytic converter 12, which is used to clean the exhaust gasesproduced by the combustion of the fuel, is disposed in exhaust pipe 8.

Fuel injector 9 is connected to a fuel accumulator 13 by means of apressure line. The fuel injectors of the other cylinders of internalcombustion engine 1 are connected to fuel accumulator 13 in acorresponding manner. Fuel accumulator 13 is supplied with fuel via asupply line. A fuel pump, which is suitable to generate the desiredpressure in fuel accumulator 13, is provided for this purpose.

Furthermore, a pressure sensor 14 by which the pressure in fuelaccumulator 13 is able to be measured is also arranged on fuelaccumulator 13. This pressure is the pressure exerted on the fuel andwhich is therefore used to inject the fuel into combustion chamber 3 ofinternal combustion engine 1 by means of fuel injector 9.

During operation of internal combustion engine 1, fuel is supplied intofuel accumulator 13. This fuel is injected into associated combustionchambers 4 via fuel injectors 9 of the individual cylinders 3. Theinjected fuel quantity is essentially a function of the injection timeand the fuel pressure in fuel accumulator 13.

With the aid of spark plugs 10, combustions are generated in combustionchambers 3 by which pistons 2 are set into a back-and-forth motion.These movements are transmitted to a crankshaft (not shown), where theyexert a torque.

A control unit 15 receives input signals 16, which represent performancequantities of internal combustion engine 1 measured by sensors. Forinstance, control device 15 is connected to pressure sensor 14, anair-mass sensor, an engine-speed sensor and the like. Moreover, controlunit 15 is connected to a driving-pedal sensor, which generates a signalindicating the setting of a driver-operatable driving pedal and therebyindicates the torque that is called for. Control device 15 generatesoutput signals 17 by which the performance of internal combustion engine1 may be influenced via actuators. For example, control device 15 isconnected to fuel injector 9, spark plug 10 and the like and generatesthe signals required for their triggering.

Among others, control device 15 is provided to control and/or regulatethe performance quantities of internal combustion engine 1. For example,the fuel mass injected into combustion chamber 4 by fuel injector 9 iscontrolled and/or regulated by control device 15, in particular withrespect to fuel economy and/or low pollutant generation. To this end,control unit 15 is equipped with a microprocessor, which has a programstored in a storage medium, in particular a flash memory, that issuitable to execute this control and/or regulation.

Control device 15 also triggers intake valve 5 and discharge valve 6, ortheir electromagnetic actuators, in order to draw fresh air intocombustion chamber 4 during an intake cycle of cylinder 3, or todischarge waste gas from combustion chamber 4 into discharge pipe 8during a discharge cycle. The present invention provides for a specialtriggering of intake valve 5 and discharge valve 6 for the directstarting of internal combustion engine 1 (FIG. 10), that is to say,without actuation by an electric starter or similar device.

To this end, as can be gathered from the state diagram in FIG. 9,internal combustion engine 1 is first brought into a start-up operatingmode 100 for a start from standstill 99, from which it transitions toidle operating mode 110 after a certain period of time. Arrow 120, drawnin as a dashed line in FIG. 9, together with the four dots in the righthalf of the state diagram, indicates that internal combustion engine 1(FIG. 10) may assume even more operating modes once idle operating mode110 has been attained, prior to being deactivated in step 199, ifappropriate.

For the purpose of illustration, the time characteristic of a triggeringof intake valve 5 and discharge valve 6 may be plotted over the crankangle, denoted by KW. Such an illustration is also known asvalve-trigger diagram or as valve-lift curve.

FIG. 1 shows such a valve-trigger diagram for a first specificembodiment of the present invention; here, the left part of the solidcurve, which extends between approximately 170° KW and 370° KW, isassigned to discharge valve 6, whereas the right part of the solidcurve, which extends between approximately 350° KW and 560° KW, isassigned to intake valve 5. In the additional valve-trigger diagrams ofFIGS. 2 through 8, the left side of the curve of the particularvalve-trigger diagram is also always assigned to discharge valve 6 andthe right part of the curve to intake valve 5. This corresponds to aportion of a regular working cycle of internal combustion engine 1 (FIG.10) in which, following a combustion (not shown) of an air-fuel mixturein combustion chamber 4 of cylinder 3 (FIG. 10), the exhaust gas isdischarged via discharge valve 6 and fresh gas is then drawn in throughintake valve 5.

The solid curve in FIG. 1 represents a conventional triggering ofdischarge valve 6 and intake valve 5, as it occurs in idle operatingmode 110 (FIG. 9), for instance.

In contrast to a conventional triggering, the present invention providesfor the discharge instant to be retarded in the first specificembodiment according to FIG. 1. This is symbolized by the dashed curvein FIG. 1, which represents a triggering of discharge 6 according to thepresent invention and is shifted, i.e., retarded, by approximately 20°to 30° KW compared to the conventional triggering. In addition, theretardation according to the present invention is illustrated clearly bythe two arrows shown in FIG. 1.

The afore-mentioned values of the crankshaft angle for the retardationaccording to the present invention are exemplary values, which may varyconsiderably depending on the internal combustion engine, the ambientconditions and the like. This also applies to all other crankshaft-anglevalues mentioned or illustrated, without restricting the universality.

The retardation according to the present invention results in a betterconversion into mechanical action of the combustion energy that isreleased during the first combustion in a direct start of internalcombustion engine, which may be utilized for starting internalcombustion engine 1.

According to another specific embodiment of the present invention, asimilar effect may also be achieved by shortening the discharge phase.In this case, discharge valve 6 (FIG. 10) is opened for a shorter periodof time compared to idle operating mode 110 (FIG. 9), for instance. Thetriggering required for the shortened discharge phase may be gatheredfrom the dashed curve in FIG. 2 where the curves associated with aconventional triggering are once again drawn in as a solid line. Incontrast to the previous specific embodiment of the present invention,the end of the discharge phase, shortened according to the presentinvention, coincides in time with the end of the conventional dischargephase. This method variant may also be used for internal combustionengines that allow a variation of only the opening durations ofintake/discharge valves 5, 6.

FIG. 3 shows another method variant in which a closing instant of intakevalve 5 is retarded with respect to the standard closing instant used inidle operating mode 110, for instance. The retardation of the closinginstant according to the present invention results from a shifting ofthe triggering of the intake valve 5, symbolized in FIG. 3 by arrowspointing to the right, such shifting once again being drawn in as adashed line.

The shifting of the closing instant of intake valve 5 provided by thepresent invention lowers the compression pressure prevailing incombustion chamber 4 of internal combustion engine 1, thereby alsofacilitating a reliable direct start of internal combustion engine 1.

An additional method variant according to the present invention, inwhich a retardation of the closing instant of intake valve 5 results, isshown in FIG. 4 and characterized by an extended opening duration ofintake valve 5 compared to idle operating mode 110, for example. Thismethod variant is also able to be used for internal combustion enginesthat allow a variation of only the opening duration of intake/dischargevalves 5, 6, but no adjustment of a triggering phase of intake/dischargevalves 5, 6.

An additional advantageous method variant is shown in FIG. 5 in whichboth the triggering of discharge valve 6 and the triggering of intakevalve 5 are time-retarded with respect to idle operating mode 110, forexample.

The same effects are also achieved in the variants of the presentinvention according to FIGS. 6 through 8, which each represent adifferent combination of the afore-discussed method variants.

In this context, the valve-trigger diagram from FIG. 6 shows acombination of the method variants of FIGS. 2 and 4, i.e., in thetriggering according to the valve-trigger diagram of FIG. 6, dischargevalve 6 (FIG. 10) is opened for a shorter period of time compared toidle operating mode 110 (FIG. 9), for example, and the opening durationof intake valve 5 is simultaneously prolonged compared to idle operatingmode 110, for instance.

The variant shown in FIG. 7 is distinguished in that the triggering ofdischarge valve 6 is shifted, i.e., retarded, by approximately 20° to30° KW compared to the conventional triggering and in that the openingduration of intake valve 5 is extended simultaneously compared to idleoperating mode 110.

The valve-trigger diagram in FIG. 8 shows yet another specificembodiment of the present invention in which the discharge phase isshortened and in which the closing instant of the intake valve issimultaneously retarded compared to idle operating mode 110 in that thetriggering of intake valve 5 is shifted relative to the conventionaltriggering.

The three last-named variants of the valve triggering according to FIGS.6 through 8 also contribute to a reliable direct start-up of internalcombustion engine 1.

In general, the retardation of the starting discharge instant and/or theclosing instant according to the present invention, used during start-upoperating mode 100, is realizable in all internal combustion engineshaving camshaft-free valve gears.

Moreover, the retardation according to the present invention is alsoachievable in camshaft-based valve-gear systems, for example by the useof phase actuators which in each case are able to adjust anintake-camshaft or a discharge camshaft.

Another specific embodiment of the present invention requires only onephase actuator, which simultaneously adjusts the intake camshaft and thedischarge camshaft. A valve-lift curve resulting in the process is shownin FIG. 5 by way of example.

In another specific embodiment of the present invention, which is basedon an adjustment of the camshaft(s), the intake camshaft and/or thedischarge camshaft are/is already adjusted during a deactivation 199(compare FIG. 9) of internal combustion engine 1 for the subsequentstart of internal combustion engine 1 in start-up operating mode 100, sothat the adjustment of the camshaft(s) required to retard the startingdischarge instant and/or the closing instant of intake valve 5 accordingto the present invention, used during start-up operating mode 100, willnot have to be implemented as late as at the next start of internalcombustion engine 1.

Depending on the means utilized to achieve the retardation according tothe present invention, it is possible to adjust a retardation that has areducing effect with increasing rotational speed of internal combustionengine 1, or an abrupt deactivation of the retardation once apredefinable minimum rotational speed of internal combustion engine 1has been exceeded.

A combination of equivalent or different phase actuators, for example aseries connection of a vane-type phase actuator known from the relatedart having a likewise known chain adjuster is also conceivable torealize the adjustment range required for the individual system.

Furthermore, in an additional specific embodiment of the presentinvention, the combination of one or a plurality of the afore-mentionedmethods with a variation of the valve lift of intake valve 5 and/ordischarge valve 6 is provided, which results in a further improvement ofthe direct start-up characteristics of internal combustion engine 1.

Although the method according to the present invention is especiallysuited for the use in internal combustion engines having directinjection, it is also conceivable to utilize the valve triggeringaccording to the present invention in internal combustion engines havingdifferent injection system

1. A method for operating an internal combustion engine having at leastone triggerable intake valve and at least one triggerable dischargevalve, comprising: directly starting the internal combustion engine in astart-up operating mode in which the discharge valve discharges anexhaust gas of the internal combustion engine; and following thedirectly starting, operating the internal combustion engine in at leastone additional operating mode; performing a retardation involving atleast one of: time-retarding a starting discharge instant of thedischarge valve with respect to a standard discharge instant used duringthe at least one additional operating mode, and time-retarding anopening instant and a closing instant of the intake valve with respectto a standard closing instant used during the at least one additionaloperating mode, the intake valve being used during the start-upoperating mode for an aspiration of a fresh gas.
 2. The method asrecited in claim 1, wherein the retardation is implemented by adjustingat least one of a discharge camshaft that triggers the discharge valveand an intake camshaft that triggers the intake valve.
 3. The method asrecited in claim 2, further comprising: using a phase actuator in eachcase to adjust one of the intake camshaft and the discharge camshaft. 4.The method as recited in claim 2, further comprising: using a phaseactuator for the simultaneous adjustment of the intake camshaft and thedischarge camshaft.
 5. The method as recited in claim 2, furthercomprising: using a valve-gear system influencing an opening time of oneof the intake valve and the discharge valve to adjust one of the intakecamshaft and the discharge camshaft.
 6. The method as recited in claim2, wherein at least one of the intake camshaft and the dischargecamshaft is already adjusted during a deactivation of the internalcombustion engine for a subsequent start in the start-up operating mode.7. The method as recited in claim 1, wherein at least one of the intakevalve and the discharge valve is triggered by a camshaft-free valve-gearsystem.
 8. The method as recited in claim 1, wherein a valve lift of oneof the intake valve and the discharge valve is varied.
 9. The method asrecited in claim 1, further comprising: decreasing the retardation in astepwise manner with increasing rotational speed of the internalcombustion engine.
 10. The method as recited in claim 1, furthercomprising: deactivating the retardation once a predefinable minimumrotational speed of the internal combustion engine is exceeded.
 11. Aninternal combustion engine, comprising: at least one triggerable intakevalve; at least one triggerable discharge valve that is directly startedin a start-up operating mode and, following the start, is operated in atleast one additional operating mode; and an arrangement for performing aretardation including at least one of: an arrangement for time-retardinga starting discharge instant of the discharge valve with respect to astandard discharge instant used during the at least one additionaloperating mode, and an arrangement for time-retarding an opening instantand a closing instant of the intake valve with respect to a standardclosing instant used during the at least one additional operating mode,the intake valve being used during the start-up operating mode for anaspiration of a fresh gas.
 12. A control device for an internalcombustion engine having at least one triggerable intake valve and atleast one triggerable discharge valve that is directly started in astart-up operating mode and, following the start, is operated in atleast one additional operating mode, comprising: an arrangement forperforming a retardation including at least one of: an arrangement fortime-retarding a starting discharge instant of the discharge valve withrespect to a standard discharge instant used during the at least oneadditional operating mode, and an arrangement for time-retarding anopening instant and a closing instant of the intake valve with respectto a standard closing instant used during the at least one additionaloperating mode, the intake valve being used during the start-upoperating mode for an aspiration of a fresh gas.
 13. A computer programfor a control device for an internal combustion engine having at leastone triggerable intake valve and at least one triggerable dischargevalve that is directly started in a start-up operating mode and,following the start, is operated in at least one additional operatingmode, comprising: instructions for performing a retardation including atleast one of: instructions for time-retarding a starting dischargeinstant of the discharge valve with respect to a standard dischargeinstant used during the at least one additional operating mode, andinstructions for time-retarding an opening instant and a closing instantof the intake valve with respect to a standard closing instant usedduring the at least one additional operating mode, the intake valvebeing used during the start-up operating mode for an aspiration of afresh gas.
 14. The computer program as recited in claim 13, wherein thecomputer program is stored on an electric memory medium.
 15. Thecomputer program as recited in claim 14, wherein: the electric memorymedium includes one of a flash memory and a read-only memory.